Multi-site RCTs have shown that every 2lbs of weight loss is associated with a 20% reduction in the 3yr risk of hypertension and a 32% reduction in the 3yr risk of type 2 diabetes. This is equivalent to the stroke risk reduction associated with smoking cessation. Unfortunately, in intervention trials dating back to 1990, black women have experienced 50% less weight loss than white women. Thus, lifestyle weight loss interventions may actually increase racial disparities in morbidity; all 5 leading causes of death among black women are obesity-related. Obesity prevalence among the urban poor is very high and obesity research in the urban poor is an IOM and DHHS priority. Starting in 2006, we worked with the 3rd largest safety-net health system in the U.S. to implement a lifestyle weight loss intervention that operates in its 8 Federally Qualified Health Centers. This program too has resulted in 50% less weight loss in black relative to white women. We also have an ongoing weight loss RCT testing the impact of delivering the intervention into the homes of the urban poor. No outcomes are available yet but it too is a person-centric lifestyle intervention. With a goal of improving weight loss outcomes, we successfully piloted a novel approach to assessing micro- environments that coincide with weight-related behaviors including momentary social interactions and emotions. Literature places a very strong emphasis on the role of social micro-environments in obesity and weight loss disparities. Individuals are often unaware of the influence of micro-environments on their behavior. For example, experiments have shown that we consume up to 70% more calories when eating with others and that we are largely unaware we have done so. Previous research suggests social networks of black women are less supportive of weight loss than are those of white women. Such social networks may lead to more exposures to obesity, food, eating, sedentary activities, and acceptance of these. In fact, a recent year-long study that captured objective assessments of social interactions among first year dormitory residents found the number of interactions with weight gaining others accounted for 1/3rd of the variance in one-year weight gain. We seek in the proposed study to assess, compare, and test the influence of social and physical micro- environments and emotions on inactivity and eating in 300 urban poor black and white women. Our Aim 1 involves novel data collection via GPS, Bite Counters, and accelerometers to obtain location and behavior data and a hybrid of ecological momentary assessment and the day reconstruction method to obtain social interaction and emotion data. In our Aim 2 randomized trial, these data are used to test hypotheses about micro-environments and weight change. Each individual's Aim 1 data are used to test whether messages in the form of health-related words and images at the time and location each woman's data indicate she is vulnerable to eating or sedentary activity affect weight change. This work will inform next-generation weight loss programs and advance our understanding of automatic behaviors in health and health disparities.